http://www.valvewizard.co.uk/smoothing.html says 50/C for each capacitor, so in your case:
Rmax = 50/220e-6 = 227k
There are many exampled which ignore this though: the 5150ii has to 330” caps in series with 220k balancing resistors, when the 50/C suggests a max of 150k should be used!
They also use 220k for the 100+100 in the screen supply when they could go as large at 470k. No doubt a case of this is what we've done before so we'll do it again.
As far what to choose, how long do you want to wait for your caps to bleed off before you can poke inside your amp?